The present invention relates to tobacco cutting or shredding machines in general, and more particularly to improvements in tobacco cutting machines of the type wherein two convergent endless chains or analogous conveyors define a substantially horizontal channel wherein tobacco leaves or portions of tobacco leaves (including ribs, reconstituted tobacco or laminae) are converted into a cake whose leader is fed into the range of orbiting shredding knives.
The channel in a machine of the above outlined character normally receives tobacco from an upright duct which is located above the rearwardly extending portion of the lower conveyor. The duct includes at least one mobile wall or rake which is moved at regular intervals to push descending tobacco particles or leaves into the rear end of the channel. At least the majority of descending tobacco particles are caused to change the direction of their movement (from substantially vertical to substantially horizontal) when they reach the rear portion of the lower conveyor or the layer of tobacco particles on such rear portion. In order to insure that the leader of the cake in the horizontal channel between the conveyors is invariably compacted to an optimum degree or that the extent of densification is within an acceptable range, the front portion of the upper conveyor is normally urged toward the front portion of the lower conveyor by means of a yieldable biasing device, such as a dashpot, a set of springs or a fluid-operated motor.
It has been found that heretofore known tobacco cutting machines are incapable of producing a tobacco cake whose consistency is sufficiently predictable to insure a continuous satisfactory shredding action. A phenomenon which is observable in presently known machines is the development of cavities in the cake. Such cavities develop in response to interruption of the shower or stream of tobacco particles which descend in the duct toward the rear portion of the lower conveyor. Another reason for the formation of an unsatisfactory tobacco cake is unpredictable orientation of tobacco particles (particularly whole leaves or tobacco leaf laminae) in the channel between the upper and lower conveyors. If the plane of a tobacco particle is substantially normal to the direction of movement of the cake toward the knives, the knives are likely to extract the entire particle without any comminuting action.
The critical zone of the path along which tobacco particles travel from the inlet of the duct toward the outlet of the channel between the conveyors is the region above the rear portion of the lower conveyor. In such region, the particles of tobacco are caused to change the direction of their movement from vertical to horizontal (i.e., through approximately 90 degrees). The particles which descend in the rear portion of the passage of the duct (i.e., in that portion of the duct which is remotest from the knives) must cover a greater distance on their way toward and into the channel between the conveyors than the particles which descend immediately behind the rear end of the upper conveyor. This results in unpredictable and widely different degree of change of orientation of particles with attendant lack of proper stratification of particles in the cake.